A variety of adhesive patches of the transdermally absorbable preparations formulated with various local anesthetics as transdermal absorption promoters for a non-steroidal anti-inflammatory analgesic have been developed and studied for many years (Patent Documents 1 to 9).
This is based on the idea that release of the absorption promoter formulated in the adhesive patch preparation promotes release of the non-steroidal anti-inflammatory analgesic, thereby resulting in an effective transdermally absorbable adhesive patch showing excellent transdermal absorption.
However, many local anesthetics are basic drugs while many non-steroidal anti-inflammatory analgesics are acidic drugs. Therefore, when these drugs were simultaneously formulated in the adhesive patch, these formed salts and inhibited drug releasing of each other thereby to fail to obtain the desired medicinal effect.